President Obama is soon expected to announce an Environmental Protection Agency regulation to cut carbon pollution from the nation's fleet of 600 coal-fired power plants, in a speech that government analysts around the world will scrutinize to determine how serious the president is about fighting global warming.

The regulation - expected Monday - will be Obama's most forceful effort to reverse 20 years of relative inaction on climate change by the U.S., which has stood as the greatest obstacle to international efforts to slow the rise of heat-trapping gases from burning coal and oil that scientists say cause warming.

The president had tried, without success, to move a climate change bill through Congress in his first term, and such legislation would now stand no chance of getting past the resistance of Republican lawmakers who question the science of climate change. So Obama is taking a controversial step: He is using his executive authority under the 1970 Clean Air Act to issue an EPA regulation taking aim at coal-fired power plants, the nation's largest source of carbon pollution.

China and the U.S., the world's two largest economies and greenhouse gas polluters, are locked in a stalemate over carbon-cutting actions. Chinese policy experts say that Obama's regulation could nudge China to act.

"If the standard is really stringent, that will make a difference in the domestic debate in China," Qi said.

The EPA rule comes at a crucial moment in the fraught international effort to slow global warming. In March, the American Association for the Advancement of Science released a report warning that human-caused climate change is leading to food and water shortages, extreme heat waves and droughts, rising sea levels and stronger storms.

"We're very excited to see the new rule on existing power plants. We see this as absolutely the backbone of U.S. climate strategy," said Günter Hörmandinger, environmental counselor to the European Union delegation in Washington.